fix(CI): reference correct github event var names

Signed-off-by: Cameron Smith <[email protected]>

.github/workflows/CI.yaml

@@ -236,12 +236,13 @@ jobs:
       - uses: rlespinasse/github-slug-action@v4
         with:
           prefix: CI_
-      - run: |
+      - name: Set git variables
+        run: |
           echo "GIT_REPO_NAME=$CI_GITHUB_REPOSITORY_NAME_PART" >> $GITHUB_ENV
           echo "GIT_REF=$CI_GITHUB_REF_NAME" >> $GITHUB_ENV
           if [ "${{ github.event_name }}" == "pull_request" ]; then
-            echo "GIT_SHA=$CI_GITHUB_EVENT_PULL_REQUEST_SHA" >> $GITHUB_ENV
-            echo "GIT_SHA_SHORT=$CI_GITHUB_EVENT_PULL_REQUEST_SHA_SHORT" >> $GITHUB_ENV
+            echo "GIT_SHA=$CI_GITHUB_EVENT_PULL_REQUEST_HEAD_SHA" >> $GITHUB_ENV
+            echo "GIT_SHA_SHORT=$CI_GITHUB_EVENT_PULL_REQUEST_HEAD_SHA_SHORT" >> $GITHUB_ENV
           else
             echo "GIT_SHA=$CI_GITHUB_SHA" >> $GITHUB_ENV
             echo "GIT_SHA_SHORT=$CI_GITHUB_SHA_SHORT" >> $GITHUB_ENV
@@ -250,7 +251,8 @@ jobs:
           echo "Using Git Reference: $GIT_REF"
           echo "Using Git SHA: $GIT_SHA"
           echo "Using Git SHA Short: $GIT_SHA_SHORT"
-      - run: |
+      - name: Build nix images
+        run: |
           echo "Using Git Repository Name: $GIT_REPO_NAME"
           echo "Using Git Reference: $GIT_REF"
           echo "Using Git SHA: $GIT_SHA"